By Jeff Mason and Roberta Rampton WASHINGTON (Reuters) – President Barack Obama and his powerful U.S. Senate adversary struck a conciliatory tone on Wednesday, but Obama’s plans to proceed with new immigration rules foreshadowed a bumpy start to his relationship with a Republican-controlled Congress. Obama and Mitch McConnell, who will become majority leader when Republicans take charge in the Senate in January, signaled they hoped to get past a previously frosty relationship to pass legislation on priorities on which they can both agree. …